Conventionally, acrylic pressure-sensitive adhesive tapes or sheets have been widely used, because they are excellent in light resistance, weather resistance, oil resistance and the like, and excellent in pressure-sensitive adhesiveness such as pressure-sensitive adhesive force and cohesive force and in antiaging properties such as heat resistance and weather resistance.
However, the acrylic pressure-sensitive adhesive tapes or sheets have not been sufficient in adhesive performance to nonpolar adherends such as polyolefins represented by polypropylene. Further, the adhesive performance to coated plates, particularly to coated plates that have recently become poor in adhesiveness by the influence of the shift to applications for acid rain resistance or aqueous systems has not been satisfactory.
There have been known techniques for enhancing the adhesive performance to these nonpolar adherends such as polyolefins, and there is disclosed an acrylic polymer in which a monomer having a specific SP value and a Tg of 15° C. or more is copolymerized (patent document 1). However, when a large number of parts of the monomer having a Tg of 15° C. or more is copolymerized, the Tg of the polymer increases to cause deterioration of low-temperature adhesiveness. Further, in such a copolymerization amount that the low-temperature adhesiveness is not deteriorated, the adhesive performance to the nonpolar adherends has not been sufficiently obtained in some cases. Furthermore, there is disclosed a method of adding a specific tackifier resin such as rosin or a hydrogenated petroleum-based resin to an acrylic polymer (patent documents 2 and 3). However, even when this method is used, the adhesive performance to the nonpolar adherends has not been sufficiently obtained in some cases. In addition, there is disclosed a method of adding an acrylic oligomer having a weight-average molecular weight of 20,000 or less to an acrylic polymer (patent document 4). However, the acrylic oligomer having a weight-average molecular weight of 20,000 or less and being capable of improving the adhesive performance to the polyolefins is poor in compatibility with the acrylic polymer used as a pressure-sensitive adhesive, and when a pressure-sensitive adhesive tape is stored for a long period of time or at high temperature, a problem of deterioration in the adhesive performance has occurred in some cases. Further, the use of an acrylic oligomer having a weight-average molecular weight of 20,000 or less and a Tg of 25° C. or more is disclosed (patent document 5). However, the use of such an oligomer results in poor compatibility with an acrylic polymer, and when a pressure-sensitive adhesive tape is stored for a long period of time or at high temperature, a problem of deterioration in the adhesive performance has occurred in some cases.
On the other hand, as a method for improving the adhesive performance to the poorly adherent coated plates, there is known, for example, a method of copolymerizing a cyclic acrylamide or an N-vinyl cyclic amide with an acrylic polymer (patent document 6). Even when such a method is used, the adhesive performance to the poorly adherent coated plates has not been sufficient in some cases. Further, it is necessary to add a polar monomer at high parts for exhibiting the characteristics, which has caused a problem of deterioration in water resistance in some cases. Furthermore, it is disclosed to use a polymer obtained from an acrylic monomer and an olefinic polymer having a polymerizable unsaturated double bond at a terminal thereof (patent document 7). However, when this technique is used, the olefinic polymer having a polymerizable unsaturated double bond at a terminal thereof has a low polymerization degree, and the rate thereof remained without being copolymerized has increased, or the conversion of the acrylic monomer has also been deteriorated in some cases. In addition, the resulting viscoelastic body has had a disadvantage such that the cohesive force is weak, resulting in failure to exhibit holding performance.    Patent Document 1; JP-A-10-509198    Patent Document 2; JP-A-6-207151    Patent Document 3; JP-T-11-504054    Patent Document 4; JP-A-2001-49200    Patent Document 5; JP-A-2003-49130    Patent Document 6; JP-A-6-200225    Patent Document 7; JP-A-2005-239831